The present invention relates generally to disease management systems, and in particular to a diabetes management system for predicting a future blood glucose value of a patient and for recommending a corrective action to the patient when the future blood glucose value lies outside of a target range.
Insulin dependent diabetes mellitus (IDDM) is caused by the auto-immune destruction of the insulin producing islets of Langerhans in the pancreas. Insulin replacement therapy is the interim treatment for IDDM until such time as islet transplants become feasible. Insulin lowers the concentration of glucose in the blood, while food raises the concentration of glucose in the blood. The challenge of insulin therapy is to administer food and insulin in a manner which maintains blood glucose concentrations in an acceptable range, thereby avoiding hypoglycemia and hyperglycemia.
Hyperglycemia has adverse long term consequences for the body. These consequences include kidney damage leading to kidney failure, micro-enurisms in the retina causing blindness, and the blocking of capillaries in the extremities causing an inability to heal wounds and subsequent gangrene. Hypoglycemia has an immediate adverse consequence of reduced brain function which leads to confusion and an inability to reason, remember, or react. In the extreme, hypoglycemia causes seizure, coma, and death.
The first insulin used by diabetes patients was regular insulin taken from beef or pig pancreases. This insulin lasts for about six hours, so that patients were required to inject it three or four times per day. After World War II, longer acting insulin was developed by binding regular insulin to protamine and zinc. Regular insulin dissociates slowly from protamine and zinc, extending insulin action to twelve hours for intermediate acting insulin and twenty-four hours for ultra-lente insulin. Patients enjoyed reducing injections to one per day, but were required to modify their eating to a snack-all-day regimen to avoid hypoglycemia. The one daily insulin dose was adjusted as needed to reduce the incidence of both hypoglycemia and hyperglycemia.
The development of portable blood glucose meters encouraged the development of more sophisticated insulin therapy regimens. One of these regimens is the split/mixed regimen which consists of two daily doses of mixed regular and intermediate acting insulins taken before breakfast and dinner. These four insulin therapy components are adjusted using blood glucose values measured before each meal and at bedtime. Patients using the split/mixed regimen are required to eat substantially the same meals every day so that the four insulin components may be adapted to the consistent meal pattern over time.
The split/mixed regimen has the advantage of allowing independent adjustment of insulin doses for each meal and requires only two injections per day. However, it has several disadvantages which are primarily due to the intermediate acting insulin components. The intermediate acting insulin taken before breakfast affects lunch time and pre-dinner blood glucose, requiring a patient to commit to the size and timing of lunch before eating breakfast. The broad action of the intermediate acting insulin may lead to hypoglycemia before or after lunch when the size or timing of the lunch is varied. Similarly, the intermediate acting insulin taken before dinner requires the patient to eat a snack at bedtime to mitigate nocturnal hypoglycemia. Even when a snack is eaten, the intermediate acting insulin may cause hypoglycemia around 3 AM when its action peaks.
Many of the disadvantages of the split/mixed regimen are overcome in a second insulin therapy regimen called the basal/bolus regimen. The basal/bolus regimen attempts to emulate the method by which an intact pancreas controls blood glucose. Normally, the intact pancreas produces a steady supply of basal insulin to accommodate the body""s basic resting needs. The pancreas handles meals by releasing a sharp impulse of bolus insulin in a first phase. The sharp impulse of bolus insulin raises circulating insulin levels immediately. The first phase is followed by a sustained level of heightened insulin release in a second phase. The second phase continues until the body""s blood glucose concentration falls back to normal, at which point basal levels are obtained once again.
In the basal/bolus regimen, the basal insulin releases are emulated by two daily basal injections of intermediate acting insulin, such as Lente or Neutral Protamine Hagedorn (NPH), generally taken before breakfast and at bedtime. The bolus insulin releases are emulated by bolus injections of regular or fast acting lispro insulin taken before each meal. Fast acting lispro insulin allows the bolus injections to emulate the first phase action of the pancreas better than regular insulin by reducing the delay before the insulin injection takes effect and by shortening the overall duration of the insulin""s action.
Thus, the basal/bolus regimen generally includes four insulin doses per day consisting of a pre-breakfast dose of intermediate insulin combined with regular or lispro insulin, pre-lunch and pre-dinner doses of regular or lispro insulin, and a bedtime dose of intermediate insulin. The two basal insulin doses accommodate the basic insulin needs of a patient absent any perturbations due to food. Food is handled by the bolus insulin doses, which the patient attempts to tailor to the amount of food to be eaten.
Problems arise in the basal/bolus regimen when a patient incorrectly estimates the dose of bolus insulin required for a given meal. Too little insulin causes the patient to develop hyperglycemia, while too much insulin causes the patient to develop hypoglycemia. Hypoglycemia or hyperglycemia may also result when the size of the meal is varied without adequate adjustment of the bolus insulin dose. Patients using the basal/bolus regimen are typically required to eat substantially the same meals every day so that the bolus insulin doses may be adapted to the consistent meal pattern over time.
Several electronic diabetes management systems have been developed to assist patients in the implementation of the split/mixed or basal/bolus regimens. One such system is disclosed in U.S. Pat. No. 5,019,974 issued to Beckers on May 28, 1991. Beckers describes a master computer for developing a therapy program for a patient and for downloading the therapy program to a patient-operated recorder. The recorder reminds the patient of any therapy due and records that the therapy has been performed by the patient. Data from the recorder is subsequently fed back to the master computer to improve or alter the therapy program.
In using Backersxe2x80x2 system, a patient must strictly adhere to the predetermined therapy guidelines in order for the therapy program to be effective. To make any therapy adjustments, the patient must upload data to the master computer, wait for the therapy adjustments, and strictly follow the adjusted guidelines. Thus, Beckersxe2x80x2 system restricts the patient to a consistent meal plan, with no flexibility for adjusting the therapy program to meals of varying size or timing.
Following a consistent meal plan is extremely difficult, whether for diabetes treatment or weight loss. Rarely can a patient stick to a predetermined meal plan every day of his or her life. Consequently, Beckersxe2x80x2 system is ineffective for assisting the patient in controlling blood glucose and avoiding hypoglycemia or hyperglycemia when the patient deviates from the plan during his or her normal course of behavior.
Moreover, Beckersxe2x80x2 system lacks any mechanism for predicting the patient""s future blood glucose concentration and is thus unable to alert the patient to future hypoglycemia or hyperglycemia resulting from an unusual meal or an incorrectly estimated insulin dose taken for the meal. Further, Beckers does not teach or describe any mechanism for recommending to the patient a corrective action, such as a supplemental insulin dose or carbohydrate supplement, when the patient has a potential for future hypoglycemia or hyperglycemia.
Another diabetes management system is disclosed in U.S. Pat. No. 4,731,726 issued to Allen on Mar. 15, 1988. Allen describes a system which includes a physician computer for downloading therapy guidelines to a patient-operated apparatus. The apparatus includes a blood glucose meter for recording a patient""s blood glucose values and keys for entering patient data relating to diet, insulin, exercise, stress, and symptoms of illness. The apparatus is programmed to recommend insulin doses to the patient based upon the data supplied.
Unfortunately, Allen""s system recommends insulin doses to the patient based upon pre-meal blood glucose values only, as stated in column 16, lines 42-44. This forces the patient to wait until the next meal before he or she may take action to correct hypoglycemia or hyperglycemia developed since the previous meal. Further, Allen""s system has no mechanism for predicting the patient""s future blood glucose concentration based upon the patient""s post-meal blood glucose value and the insulin action remaining from insulin doses injected before the meal. As a result, Allen""s system is unable to alert the patient to future hypoglycemia or hyperglycemia resulting from the patient eating an unusual meal or taking an incorrect insulin dose for the meal.
In view of the above, it is an object of the present invention to provide a diabetes management system for predicting a future blood glucose concentration of a patient based upon the patient""s current blood glucose concentration and the insulin action remaining from previous insulin doses, thereby enabling the patient to take timely corrective action to prevent hypoglycemia or hyperglycemia. It is another object of the invention to provide a diabetes management system for recommending the corrective action to the patient when the predicted blood glucose value lies outside of a target range.
These and other objects and advantages will become more apparent after consideration of the ensuing description and the accompanying drawings.
The invention presents a system and method for assisting a patient having diabetes mellitus in controlling blood glucose. The system includes a patient-operated apparatus having a blood glucose meter for measuring a blood sample of the patient and for producing from a measurement of the blood sample a blood glucose value G(td) representative of a blood glucose concentration of the patient at time td. The apparatus also includes a user interface for entering in the apparatus an insulin dose value Ik representative of an insulin dose administered to the patient prior to time td. 
The apparatus further includes a memory for storing maximum and minimum values defining a target blood glucose range of the patient. The memory also stores a target blood glucose value of the patient within the range, an insulin sensitivity value representative of an insulin sensitivity of the patient, and information for determining an insulin action value Fk(td) representative of a fraction of insulin action remaining at time td from the insulin dose.
A processor is connected to the glucose meter, user interface, and memory. The processor is programmed to determine the insulin action value Fk(td) and to determine a future blood glucose value G(tj) representative of an expected blood glucose concentration of the patient at time tj. The processor determines the future blood glucose value G(tj) in dependence upon the blood glucose value G(td), the insulin dose value Ik, the insulin sensitivity value, and the insulin action value Fk(td). The processor is also programmed to determine a corrective action for the patient when the future blood glucose value G(tj) lies outside of the target range.
The corrective action is preferably an administration of a supplemental insulin dose when the future blood glucose value G(tj) lies above the target range or a consumption of a number of grams of carbohydrates when the future blood glucose value G(tj) lies below the target range. The processor is programmed to determine the supplemental insulin dose in dependence upon the insulin sensitivity value and a difference between the future blood glucose value G(tj) and the target blood glucose value. The processor is further programmed to determine the number of grams of carbohydrates to be consumed in dependence upon the difference between the future blood glucose value G(tj) and the target blood glucose value. A display is connected to the processor for displaying the future blood glucose value G(tj) and for recommending the corrective action to the patient.
The system also includes a healthcare provider computer in communication with the apparatus for receiving from the apparatus blood glucose values and insulin dose values and for calculating from the values an adjusted insulin sensitivity value for the patient. The apparatus includes a communication device, such as a modem and input/output port, connected to the processor for establishing a communication link between the apparatus and the healthcare provider computer, for transmitting the blood glucose values and insulin dose values through the communication link, and for receiving through the communication link the adjusted insulin sensitivity value.